Well, what he must do is make sure he is ahead before WTF. If he is ahead just before, he cannot lose No. 1 even if Nole wins WTF and Nadal doesn't participate.

To do that, he must make sure to earn more points than Nole in Basel/Valencia and Paris. He will take an advantage with Shanghai here. If he wins Shanghai, he will be at least 1440 points ahead of Djokovic and cannot mathematically lose No.1 this year. Even if he doesn't win, he needs a final in all 3 events remaining to stay just 40 pts ahead of Nole, if Nole wins everything.

Example:

Shanghai:Nadal (F) = 11760Nole (W) = 11120

Basel/Valencia:Nadal (F) = 12060Nole (W) = 11620

Paris:Nadal (F) = 12660Nole (W) = 12620

This scenario is enough to keep Nadal at No.1. Obviously, if he does worse than this and Nole wins everything until WTF, Nole can secure World Number 1 before WTF, and WTF will decide to YE #1. But even if Nadal does the worst possible into WTF, he can still re-get to World Number 1 if he wins WTF:

have you people heard of Nancy Kessel? (the milkshake murderer)? She is an Amercian who lives in Hong Kong. She killed her hubby brutually by asking her daughter to serve him a milkshake that was full of seductives and when he was sleeping, cocked his head with an ornament and killed him.

Despite of being sentenced to life prison by two trials, she still does not give up and is trying her 3rd trial, wasiting her old parents and tax payers' monies. I just don't understand, didn't y think of the consequences before you did the murder? Why to deny it if proved guilty, shameless woman, i just hate this injustice thing